Field of the Invention
This invention relates to an apparatus and process for forming a shrink-wrapped package. References
U.S. Pat. No. 4,041,674, issued to Reid on Aug. 16, 1977, discloses an apparatus for packing articles, such as bottles, in units with the articles in each unit arranged in parallel rows, each row comprising a plurality of articles arranged side-by-side, said apparatus including a means for supporting articles for arrangement in rows; means for movement in a predetermined path; a pusher for pushing rows of articles on said supporting means forward generally at right angles to the length of the rows, a guide movable forward and back with the pusher and spaced forward of the pusher a distance such as to provide a space for a row of articles therebetween, and means for feeding articles in single file one after another over said supporting means from one side through said space.
A number of patents., including U.S. Pat. Nos. 3,047,140, 3,027,300, 3,272,302, 3,326,369, 3,344,975, 3,442,436, 3,654,829, 3,804,235 and 4,586,312, disclose shrink-wrapped packages having a tear tab or perforations for ease of opening or access. U.S. Pat. No. 3,016,131, issued to Kennedy, discloses a heat-shrink package of polymeric film which is provided with a desired slit pattern which opens when stretched in the heat-shrinking process.
U.S. Pat. No. 4,139,099, issued to Daly, et al. al. on Feb. 13, 1979, discloses a shrink-wrapping kit for artwork comprising a mounting board means having a face coated with adhesive for securing the artwork to the mounting board, a shrink wrap envelope slightly larger than the mounting board means formed with a flap along one side for enclosing the mounting board with artwork attached, and means for sealing the envelope flap to the envelope. The patent discloses that 150 gauge shrink film is preferred, such as W.R. Grace's "Cryovac" film, Reynolds' "Reynolon" film, and Du Pont's "Clysar" polyolefin film.
Numerous apparatus have been developed for forming shrink- wrapped packages. In one such device, a film sheeting is unwound from a roll by a powered unwind/dancer roll system through a pneumatic hole punch assembly and to a film former. Film is formed into a rectangular tube with a bottom overlap as it follows the geometry of the former. A start-up vertical heat seal is made by separate energizing of the heat sealer thereby closing the end of the film. Cartons are queued on a constantly running infeed conveyor. When a preselected number of cartons at the head queue are in an appropriate position, a proximity switch is energized thereby activating a pusher which moves the preselected number of cartons transversely to a center line above a ram. When the ram is fully retracted, the preselected number of cartons drop to the same elevation as and in front of the ram. On its forward stroke, the ram pushes the cartons through the former so that the forward most carton strikes the start-up vertical seal and thereby pulls the film forward. At the end of this stroke, the last carton has passed the heat sealer with sufficient clearance to permit activation of the heat sealer to complete the rear seal of the package and the start-up seal of the next package. On return of the stroke of the ram, the heat sealer closes to form the end seals. Upon opening of the sealer, a conveyor is activated to transfer the resulting package into a continually running heat shrink tunnel.
Operation of the foregoing prior art device requires a low shrink force packaging material, such as polyvinyl chloride, with an ability to block or mat and form a bottom lap seal in the heat tunnel. Also, high slip over the film former and quick setting of the vertical heat seal is critical to withstanding the impact and film advancement of the forward stroke of the ram. When attempts are made to use high shrink force films, such as polyolefin films, in this prior art apparatus, it was found that the polyolefin film package failed to form a bottom seal when it went through the heat shrink tunnel. Thus, there is a need for an apparatus that will shrink-wrap package an array of articles using a single web of polyolefin film.